ESC/Motor draw/Battery choice

[lainchy]

Hi,

General question here.... not only heli related....

When I built my HK450GTv2, I chose 2200mAh 3s, with a 40A esc, and a motor that draws (according to the write up) 35A peak.

Now, I've bought another plank... Dynam Hurricane. This has come with a 40A esc, but the motor spec is allegedly 60A peak

Surely, the peak draw of the motor shouldn't exceed the ESC?

How does this work? Will the motor only be able to draw the max from the esc? or will the esc struggle and be well past it's limit? Difficult to explain... will the motor be driven to 40A and that's it, or will it try and draw 60A? Surely the latter is BAD BAD BAD??

At the moment, I'm thinking the esc in the plank is gonna be hot when it's been flown? The one in my heli is only just warm

I used to fly IC years ago, so this electric game is all new to me.

Ta

[Andy01]

The motor will only draw as much power as it needs. Amps are relative to voltage, so what voltage are you running on the plank ?

I think (but have no first hand experience) that most planks pull a LOT less power than a similarly sized heli.

In general if you tried to pull a continuous 60A out of an ESC that was only rated for 40A continuous, it would probably not end well, but it all depends on how you fly and how much power you will actually use.

If you have a motor that can pull 60A and 40A ESC, but you generally fly using 25A, then you are unlikely to have a problem.

Colin

[lainchy]

Cheers Colin,

It's a 4s 3300. I guess I'll know more when a buddy of mine hooks it up to a watt meter, but I'm with you when I think there'll be less draw than the heli. The heli motor has to support the weight of the model all the time, but the plank only has to pull its drag round, so should be less.

It just confused me a bit... why put a 60A motor on a 40A esc.

Plenty of them out there though, so they must be OK. People just complaining about the pulsing of the esc at slow speed/start up.

I can live with that.

Cheers

[simplechamp]

Motor ratings can be a misleading thing. Take for example your motor that says "Max 60A". This is not some magic number that the motor will not exceed. In one aircraft it might never see more than 30A, while in another aircraft it could be overloaded to 90A and burn up. It's the prop, gearing, voltage, flight style, etc that will determine the current draw. So it may be OK to use with a 40A ESC, or it may not, really depends on those other factors.

Likewise, a 40A rated ESC will not limit the current to 40A. If you put a monster prop on that loads it up to 100A the ESC will deliver 100A (and probably thermal shutdown or burn up!)

So the key thing to remember is these current values are what the motor/ESC is rated to run safely without damage. Not a hard limit that it won't exceed. In general if you match the current ratings on motor and ESC it should perform fine providing you use the recommended props, cell count, and aircraft size. But there are always exceptions to this. Current ratings can be exaggerated because as consumers we always want to see bigger, faster, stronger, etc. It's a numbers game and every mfgr. wants to list their motor as being the most powerful. You should rely on temperature of the components as your main indicator if the setup is running OK or being overloaded. Also the wattmeter like you mentioned is a good tool to review how the system will run. Datalogging is good for this also. I really like reviewing datalogs to see how the system is performing and make sure everything is running within safe limits.

[lainchy]

Thanks Simplechamp!

That's answered plenty of questions

Many thanks